imbreeding depression

7/30/2019 imbreeding depression

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Inbreeding Depression

Fact or Fiction about Inbreeding

There has been, and still remains among many animal breeders a fear of Inbreeding versus the

accepted view of line breeding or Out crossing as a way to improve their stock. As I have

stated many times in the past, the term Inbreeding, as well as Line-breeding, are merely amatter of closeness in terms of their genetic relationship. For that reason, when I refer to

inbreeding in this article, it will represent the progeny of genetically close relatives, regardless of

terminology. I am sure we have all heard the horror stories this type of breeding can render likedeformities, poor fertility, smaller size, and general lack of vigor, as well as unfit individuals to

name just a few. If we put all these in a box, we would have the products of Inbreeding

Depression...

Lets look at this term Inbreeding Depression a little closer. This definition usually is used todescribe a given population of plants or animals that are so confined in their environment and

their given genetic pool, that this inbreeding of relatives results in more recessive deleterious

traits manifesting themselves . The more closely related the breeding animals are, the moreHomozygous Recessiveness the offspring may become, and increasing the more risk of unfit

individuals. What seems to be misunderstood is the fact that these features can be overcome by

the use of Genetic Purging or more commonly known as Culling?The other theory is one of over dominance of heterozygous alleles which is a reduction of

homozygous genotypes. Remember, we are talking about Homozygous Recessive genes taking

over the given population and rendering many of them unfit. We also must recognize that this initself is considered a most severe degree of inbreeding with no intervention from outside forces.

The same could be said about out breeding enhancement, which we will touch on later in the

article.

As breeders, we all strive to improve our stock for the betterment of the breed itself, and for

personal achievement. We first need to understand what we strive for and how to transform this

from theory to a living creature. We do this by having a clear understanding of our idealspecimen in terms of traits and characteristics that would represent the Breed in question. We do

this through the close mating of relatives, and this is known in livestock circles as Inbreeding.

Inbreeding itself is not enough to achieve our ideals. There must be strict selection and cullingof all unwanted traits and characteristics to achieve our goals. I practice a lot of close breeding,

and for the most part have had very good success with this form of breeding. This year was like

many others, and I paired a father/daughter together like I have done many times before without


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any unwanted results from the visual perspective. The parents have both been proven in terms of

their flying ability and have flown better than 16:30hrs and I was hoping that I could fix that

trait into their progeny through the forces of inbreeding. Well, as you can see in the picture # 1below, I was quite unhappy at their visual appearance at a very young age of their development.

They were small, their feathering was very inferior at this point and this was in my opinion a

direct result of Recessive traits showing themselves, picture # 2, shows a pair of squabs withnormal development. Would picture # 1 qualify as a form of Inbreeding Depression?

Now if you are of the informed breeders, you will understand that both the hen and the cockcontribute 50% of their genetic makeup randomly to their offspring. And for that reason, the

genes from each parent that are responsible for their development showed themselves in a

recessive state. Remember that when inbreeding, one can get good or bad traits as a result of

such mating.

Another fact the needs to be noted is, that if reckless inbreeding is practiced with little regard to

what is being produced, and given enough time in terms of generations that it will Fix these

recessive traits in a Homozygous form and render most, if not all that occupy the loft unfitweather it be for show purpose or performance or both! This would result in only one avenue left

for the breeder to follow, and that is the culling of all stock and a fresh start. This is whyselection for both wanted and unwanted specimens must be followed. This also gives rise to ones

Ideals as one must know what to select for.

Picture # 1 Picture # 2

Now after saying all that, here is another father/daughter mating below, slightly older but neverthe less not showing any signs of development depression. Both are fully clad as they should be

and looking great. This particular pair of young birds was doing 10 workouts when the kit flew

over and subsequently was stocked.


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So, I have only just given a brief outlook on a minor form of Inbreeding Depression The

question remains Fact or Fiction. Before you answer that, I feel there are other factors that shouldbe revealed, touched on and put in a manner that can be more widely understood.

To further ones understanding, one must have a general understanding of the term Inheritancewhich goes hand and hand to further ones knowledge about Inbreeding Depression and terms

of breeding that are generally used such as Inbreeding, Line-Breeding, and Out crossing

When Gregory Mendel first discovered the laws of Inheritance he really discovered the

complex workings of a living animal or plant. He discovered the blueprint of Inheritance, and

how it all came together. Every living thing is made up of thousands of cells called genes, andthose genes in turn are arranged in countless pairs on Chromosomes.

Now, we all claim to understand the term Trait right, but do we really? What is beingrepresented by the term Trait?

The Fact is that every pair of genes, on every chromosome, which varies depending on whatSpecies of creature we are referring to are responsible for a given Trait or portion of Trait.

It also depends on whether one or both genes are of that pair is dominant or recessive. A

dominant gene when paired with its complementary recessive gene will dominate theexpression of the trait governed by the pair. For our understanding what it is saying is that it will

mask the expression of the recessive gene.

Mendel explained that Dominance had three possible configurations for every pair of genes:

they both could be dominate (homozygous dominate), both could be recessive (homozygous

recessive) and lastly one could be dominate and one recessive.Now when breeders talk about Purity what they are saying is that a creature is Pure for a

given Trait, or Homozygous Dominate!! When they state the term Impure for a given Trait

they are saying it is Heterozygous, and lastly there is Homozygous Recessive,( Pure} These are

genetic terms that represent the law of Dominance, with me adding the words Pure and Impurewere required to try and make it a more friendly term of understanding.


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It is of grave importance that any breeder has at least a good understanding of terminologys and

their meanings if they are to be able to go forward with any breeding program with success.

When this is grasped, one can see through inbreeding, what we are really doing in fact ispurifying the traits we seek, and intensifying the speed of witch this happens by mating our stock

Closer than many would consider. A bird or animal can never be to Pure for Traits we

seek, assuming of course we have a clear understanding of what we seek in terms of our Ideal.

As I stated earlier, when a given population is deprived of genetic diversity, and are govenered

by no outside intervention, inbreeding depression may occur if and when Homozygosity hastaken over the population and created largely Homozygous Recessive individuals, it would take

countless generations to reach severe degrees of depression, rendering much of the population as

unfit individuals.

Deprived genetic diversity, or extreme population bottleneck, are the basis of how

inbreeding depression seems to occur, but there are scenarios that suggest the contrary in certain

respects. I ran across an article about a little bird called Black Robin or Chatham Island Robin.

This bird was first recorded in 1872 by Walter Buller on Chatham Island off the coast of NewZealand. As the research states, in 1980 only five Black Robins survived on Little Mangere

Island, and were saved from extinction by a fellow named Don Merton and his team, and byOld Blue the last remaining fertile female. Old Blue was the only fertile female to start with,

inbreeding was inevitable, and the fear of inbreeding depression was on the forefront Old Blue

and later from her, more fertile females were produced and today there are 250 Robins, a highlyinbred species saved from extinction. Now you may be asking what the point of this is, the point

is that all the surviving Robins are descendants of Old Blue, and due to that there is very little

genetic variation among the population and creating an extreme population bottleneck a term

we started this with. Whats interesting about this is, that all this lack of genetic diversity amongthe 250 robins has caused no, thats right no inbreeding depression! The speculation was that

through their evolutionary past, populations were reduced, and along with that so were many

carrying deleterious alleles. What must be recognized, from this outcome is that through thepowers of Selection, whether they are Natural or Artificial, inbreeding depression need not be

a factor of In-breeding. Fact or Fiction??

Black Robin (below)


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In another case of extreme bottleneck population in terms of genetic diversity being so low and

the worry of inbreeding depression rising to the surface would be the story of the Mauritius

Kestrel. This small bird of prey, weighing a mere 250grams is found only on the island ofMauritius in the Indian Ocean. In pre-colonial time the population was estimated at 175-325

breeding pairs. This small population was thought to exist due to the fact of natural causes like

cyclones and deforestation, predators and the worst being the introduction of DDT back in 1950and 1960s. Now the amazing thing about this story is, that in 1974, the population had been

decimated down to only 4 individuals, and was considered at the time, the rarest bird in the

world. Initial attempts to raise eggs artificially all were in vain as the eggs were infertile. Notuntil 1979, was a new attempt made by Gerald Durrell. Carl G Jones established a sanctuary and

climbed trees to remove eggs from the nests, and this time they were fertile, and hatched in

incubators. By 1984 the estimate was 50 individuals, pretty amassing from only 4 individuals.

Natural causes had almost rendered this species extinct if it were not for the intervention of man.Today according to (Bird Life International 2006a, b) there are more than 800 birds and rising.

As with the story of the Robin, near panmictic conditions like volcanic activity, habitat loose,

availability of food, all played a role down through the ages of generation after generation.

Through all these obstacles they managed to sustain, but there numbers suffered keeping theirpopulation small. Again, speculation suggests that deleterious alleles that may have caused in-

breeding depression were removed through natural selection.This is another example of the powers of selection, whether it is through Natural Selection, or

Artificial Selection. In-breeding depression need not be the outcome when dealing with very

small gene pools such as the two examples we just learned about.

Mauritius Kestrel

On the flip side of inbreeding and Inbreeding Depression, there is what is known in genetic termsHeterosis, a term that represents selective breeding also. This is the opposite of Inbreeding

Depression, and is also known as Hybrid Vigor or Out breeding Enhancement. The

hypothesis is (over much controversy, same as Inbreeding) is that it will produce superior


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individuals by this new combination and mixing of the parents genetic make-up. I think we have

all seen the results of this Hypothesis in the dog world; yes there is many a person cross breeding

recognized breeds of dog to create the new Yuppie or Designer Dog commonly called aMongrel!! Todays Designer Dog, or shall I say Dog by Design all started in the 20 th century for

strictly monetary reasons.

The problem with Hybrid Vigor is that for the most part it doesnt work as well as inbreedingwith sound selection. When different Species are crossed, their new genetic codes are so

mixed, and so vast, that when they themselves produce offspring, there is no consistency of

animal in terms of size or Type, or what it will look like as some of them take on characteristicsof one parent while others take on characteristics of the other parent... Superiority has been

proven only in a few instances, such as the Mule, in terms of their work abilitys (and they are

sterile and unable to perpetuate themselves) a crossing of a horse and a donkey... The above

describes the issues when distinct Breeds or Species have been crossed, but there still lies thesame problems when two distinct Strains of a given breed are crossed normally called out

crossing. Although there may be the occasional great specimen arise from this type of gene

crossing, they are far and few between in terms of superiority and they are short lived. Further

more, they may seem similar in appearance and even performance, but they will be largelyHeterozygous for gene pairs controlling those features, and their genetic impurity will make

them inconsistent breeders. The fancier can not, with any certainty predict the outcome of furthergenerations in terms of prepotency. On the flip side of this scenario any particular pair of genes

that are Homozygous, whether they be dominant or ressive, the same process occurs, but with a

confident result in terms of predictability. When youre Sire or Dam has a large number ofhomozygous gene pairs for the ideals you seek, they have become the pre-potent breeders you

seek, and are the reason for the high degree of consistency in their progeny. Their genetic purity

turns probabilities into predictabilitys. It all comes down to Selection of ones breeding

population. Is this Fact or Fiction I ask you?

The Liger shown below is the crossing of two Species of cat, the result of a mating between

a male lion and a female tiger. This is one example of classic Hybrid Vigor in the truest senseof the term. As you can see when the genetic codes of a Lion and a Tiger are mixed, the

offspring can become distorted in many ways like size or looks. Here, this Hybrid is growing to

gigantic proportions, far from its genetic ancestry of either parent. On the flip side of this mating,female offspring are dwarfed in terms of size. As stated earlier, there is no predictability or

consistency from such mating. In this case the males are sterile, but the females can be fertile in

some instances.


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To further discard the notion that inbreeding is the sole cause of unfit individuals, I would like toshare with all of you a Fact, and that is about a woman by the name of Miss King, who has

been pairing brother and sister ( the closest form of inbreeding ) rats together for over 250generations. She did this using strict selection, and created a family of rats that were not only

larger than normal, but are superior in producing greater litter sizes, greater fertility and are

indistinguishable from one another, a True Strain in my opinion. Some of you may already

have heard of this experiment by Miss King, as this article is noted in many books.

What the inspiring breeder must do is understand his Ideals, and cull all others as their

unwanted recessive traits show themselves. As both the Sire and the Dam equally pass on50% of their genetic make-up randomly to their offspring as part of the inheritance process, our

hope is to intensify their genetic make-up on the Dominant side that meets our Ideal. Themore Dominant Traits we have that meet out Ideal, the more pure the specimen becomesgenetically for those Ideals we seek. When one chooses to constantly introduce outside stock

of further unknown genetic heritage, it is the opinion of many breeders that support inbreeding

that there is no better way to further mask recessive genes, and by doing so make your job of

finding and identifying those gene pairs that are Dominate for the traits and characteristics youseek.

Under the law of Independent Assortment, Mendel sated that all genes and chromosomes areinherited independently of each other; the task of the breeder is to try and sort out all the pieces

that comprise his ideal specimen. Knowing also from Mendels writings about the Law of

Segregation, where he states that all genes, being dominant or recessive maintain their separateidentity throughout the reproductive process. If one agrees with Mendels law of inheritance, we

know that all genes are inherited in pairs, one from each parent in a random fashion, and are

responsible for one given trait, one can begin to see the task that lie before them in terms ofisolating certain genes that form ones ideal. With this in mind, it is soon realized that with every

new introduction of genetic material into ones stock only multiplies the task of unmasking all

unwanted recessive traits and characteristics. What must be brought to bear in the minds of all


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fanciers is the fact that they are the builders of their ideal specimen, the genes and chromosomes

are their building blocks. The same was said in the movie Jurassic Park, and very true.

Speaking of being the builders of ones ideals, I think it is worthy to make mention of twogenetic terms that are always being thrown around in discussion, but with very little

understanding of the terms themselves and how they relate in part to this article.

Each and every creature is actually two, the one you see standing in front of you, and the one youdont see hidden within that same creature. The first is known as Phenotype the one you see,

and the other is known as Genotype the one hidden within.

I could try and give a definition of both, but I think Professor John Blamire sums it up quite

grand and is as follows: Phenotype, This is the outward physical manifestation of the

organism. These are the physical parts, the sum of the atoms, molecules, macromolecules, cells,

structures, metabolism energy utilization, tissue, organs, reflexes, and behaviors; anything that ispart of the observable structure, function or behavior of a living organism.

The second is Genotype, This is the internally coded, inheritable information carried by all

living organizisims. This stored information is used as a blueprint or set of instuctions for

building and maintaining a living creature. These instructions are found within all cells (theinternal part), they are written in a coded language (the genetic code), they are copied at a time

of cell division or reproduction and are passed from one generation to the next (inheritable).These instructions are intimately involved with all aspects of the life of a cell or an organism.

They control everything from the formation of protein macromolecules, to the regulation of

metabolism and synthesis. As I stated earlier, each creature is really two, the one within genotype are the codes that are

responsible for the building blocks of the one we see, Phenotype, this is the very important

relationship of all living beings, and the facts about inheritance...

I am sure most , if not all of you have heard of the famous Jenson brothers, who over many

generations of inbreeding, along with very strict Ideals and culling, created a Strain of racinghomers that are renowned the world over. Their racing abilitys are so renowned that their stock

is highly prized in the eyes of others. If one was to check, I am sure that in every homer loft

around the world there has been a Jensen bred bird used with the hopes of improving their ownstock. Their Genetic Purity for certain traits is a product of inbreeding, and in turn sought after.

To further justify, and lay to rest these largely Fictitious thoughts about inbreeding I offer

testimonials of other noted breeders of livestock and their practices.


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Eugene Davenport:

No other system of breeding has ever secured the results that Line-Breeding (and Inbreeding)

has secured, and if the present state of knowledge is reasonable sound, no other system will everbe so powerful in getting the most possible out of a given breed or Varity, especially of animals,

and this with the greatest certainty as we go along. The only requirement is not to abandonindividual selection

Chandler Grover is a breeder of Rollers and states the following:

I have been breeding one family of my Penson Rollers for about 14 years that have been many

generations of brother and sister mating, or always closely related nearly as much. This only

works in a family that does not have hidden defects. Mine luckily did not throw misfits andrejects. Last year I tried another pair and raised all bad ones, blind weaklings and such. Only way

to find out is to try and I am a fellow that to try and find out for himself

Hey this is a guy after my own heart LOL!!

Dr Carl A. Naether, from his Book of the Racing Pigeon a quote from Violette, a famous

Belgian racer the following is stated:

To breed from a type, but from a type of quality, mated with a near relative, likewise of quality:

to maintain the quality, the highest level of quality, at each generation and in all generations; toselect stringently according to the principles laid down, such, I think, are the observations which

most nearly approach what a pigeon fancier should know and put into practice to obtain tangible

results in the breeding of a strain


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You have just heard the testimonials of noted breeders and their beliefs and practices on the

theory of inbreeding. They do it with an informed understanding of their Ideal specimen, andhow to achieve it. They do it without fear, but with confidence and superior results. They speak

of recessive traits showing themselves from time to time, but their knowledge, weather it is booklearned genetics or practical breeding skills; their animal sense keeps them on a path that has

proved to be the best way of attaining excellence in their stock, and that is inbreeding. Again,

is this Fact or Fiction?

If we travel back now to picture number #1, I was going to cull both of these ybs, but there were

those that offered up suggestions on what I could do to improve them, or that I was wrong in mythinking. There was even those that asked my why I would cull them, and to give them a chance

like my friend Mick Hoskins over in Australia. I told him I had no time to waste on infior quality

pigeons when I had others of much greater quality to deal with. Well for some reason I didntcull them, (see Mick, my heart is not solid stone LOL!!) and they have almost completely gone

through their first molt. I offer them to you now as they are, after months of development.

Remember, these are the products of a father/daughter mating of witch I have done many times

with great success. The family resemblance between these two cocks is so diluted; they sharelittle family resemblance in terms of Type a sure sign of genetic impurity. This genetic

Impurity or recessive traits are being unmasked if you will, rather than ones that are

genetically pure for those traits. As we see them pictured below, we could be looking at theoutcome of recessive deleterious traits or, the early signs of Inbreeding Depression in this first

generation between full brothers. Their different phenotypes suggest genetic impurity. The red

mottle has received more Homozygous Pure traits that express its phenotype than its full

brother the black mottle in terms of family related resemblance and Type He is moreHeterozygous or Impure for those traits and characteristics than his red brother. What must

be kept in mind as fact is that every individual can only become what they have received

through Inheritance from both parents when the sperm and the egg unite. In each an every caseof a new life beginning, it is only potentially what it is bred to be.

Is this phenomena Fact or Fiction, in terms of inbreeding, and a direct cause of depression?


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Earlier in this article I made note to how and why inbreeding depression would occur. As stated

earlier, this would be a result of a population lacking genetic diversity due to certain conditions

like a confinement within a given environment. Normally natures way of dealing with this

would be through Natural Selection , but in scenarios such as I have described, most of theoffspring would carry some deleterious traits and therefore, and given enough time, the average

of unfit individuals would be greater than the average of the population in question. As

inbreeding tends to have a multiplying effect genetically speaking, the outcome of fixingtraits whether they be good or bad is realized. One can see how inbreeding depression would

occur. Fact or Fiction

To further give rise to Natural Selection, Charles Darwin, his book, The Origin Of Species theGuru of evolution by many, suggested that natural selection may or may not take place

depending on their conditions of witch these individuals find themselves. Factors such as habitat,

nourishment, perspective mates, as well as disease and predication all perform a role in

Selection. He also suggests that selection occurs in a given population, when they are diverse in

characteristics, and when the traits differ in individuals in terms of how well they equipthemselves to survive a particular pressure of their environment (Survival of the Fittest) takes

president.In contrast, Artificial Selection, differs in the sense that long ago, breeders of all types of

livestock soon realized they could, through breeding for certain traits capitalize on traits,

behaviors and characteristics that they seek in a given individual. This exploitation of artificialselection has been in existence since early man and in many cases unintentional as it were. This

selection process was deemed by Darwin as a wider process of natural selection, one that had

human influences and preferences that intern give rise to significant effects on domestication. In

effect, we could through inbreeding create our own Ideals of what domesticated livestockshould look and perform like.

For those that still may have some concerns of inbreeding depression caused by inbreeding, I canoffer you this as well. This up-coming season I will be putting the product of a second generation

father/ daughter breeding back to her Sire. This is, as many would state close inbreeding, but

in my opinion this is the only way to truly create a strain, as well as change the looks of a givenspecimen to more closely represent what one is after, in this case her Sire. With each passing

generation, the offspring are getting more Homozygous pure for traits and characteristics we

seek, rising in their excellence, and genetic purity.


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The original hen I used was loaned to me by my buddy Oskar, and she was of different Type

than my stock, a Type that differed some from my personal ideals, but to her credit was from

Irish stock of a noted breeder, and her excellence was still to be realized, in terms of an out-crossas she was never flown or bred. The process of close inbreeding, and selection of tested ybs will

be done for at least 6 generations, or until I am happy with the results of this breeding program.

So far, I have flown the young birds very well in terms of performance, no signs of inbreedingdepression and the selection process has started to move closer to the Sires characteristics, or

Type shall I say. It must also be stated, that when ever intensive inbreeding is practiced, there

is bound to be recessives come to the surface, a direct result of the parents genetic make-up, andhow pure they are in terms of Ideals we seek, whether they are good or bad. If one should find

that the bad out does the good, the entire program should be scraped, as well as all the progeny,

presumably due to unfit individuals.

As with the scenarios descried above, and our understanding of Artificial Selection, our lofts are

in effect a confinement of environment in terms of implications of inbreeding that leads to

inbreeding depression. As documented, as well as my own beliefs, inbreeding depression does

exist under natural conditions as well as artificial ones. Only under the watchful eye of theinformed breeder, along with the use of sound selection, culling of all unwanted recessive traits,

(Deleterious Alleles) and testing of progeny, can a positive outcome be realized.

I would like to acknowledge the many people and books already stated in this article that were inpart, responsible in its making . Also in acknowledgment are the following: G. H. T. Stovin, his

book Breeding Better Pigeons, Genetics Made Simply by Paul P. Cook Jr. The internet as a

research engine of information, Charles Darwin book, On Natural Selection, BirdLife

International plan 2001-2011 (PDF). And finally my own practical breeding experience ofvarious livestock, and through discussions from other fanciers on this subject that are always on

the winning side.

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